STA Mastery · All levels

Delta Delay Mechanism: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Delta Delay Mechanism.

Step-by-step analysis walkthrough

Use when you own Delta Delay Mechanism in a timing war room.

Open signoff scenario list — note worst WNS corner.
report_timing -max/-min on failing group.
Trace launch and capture clocks on critical path.
Check exceptions and generated clocks on path.
Break down cell vs net delay.
Compare implementation vs signoff view if delta suspicious.
Assign owner: RTL, synth, PD, CTS, SI.
Propose ECO with hold/SI check plan.
Run regression matrix.
Update closure dashboard and memo.

Artifacts to collect

SI report, coupled net list, delta delay histogram
SDC file
SPEF tag
MMMC scenario list
ECO ticket

Decision memo template

diagram

STA DECISION MEMO — Delta Delay Mechanism
corner/mode:
WNS/TNS:
hypothesis:
ECO:
regression:
owners: SI owner, STA owner, extraction owner

Reference visuals

Aggressor / victim coupling

diagram

VICTIM NET  ~~~~~~~~~~~~ (quiet)
AGGRESSOR   ^   ^   ^   ^  (switching)

Aligned switching -> delta delay on victim
SI analysis adds coupling to effective RC

STA deep dive

Coupling makes delay a function of neighbors, not just wire RC.

Concept diagram

diagram

SI ON VICTIM

victim net delay = base_RC + coupling_from_aggressors

Metric graph

diagram

DELTA DELAY ON CRITICAL PATHS

no SI   ████████  1.2ns
with SI ██████████  1.35ns  (+150ps)

Reports and artifacts

delta delay report
aggressor list
noise peaks
SI WNS delta

Mini case study

Setup fixed by upsize but SI worsened — spacing ECO on bus bits recovered margin.

Debug branches

Re-run SI after every timing ECO
Shield wide switching buses

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

State corner, mode, view, and database tag with every slack claim.
Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

Comparing STA runs with different SPEF or SDC tags.
Broad false_path to green-wash violations.
Setup-only ECO without hold check.

Principal STA review addendum

Coupling capacitance between adjacent nets changes effective delay; aggressors slow or speed victims depending on switching alignment.

Metric: delta delay on critical paths, aggressor count, SI WNS impact

Practice this lesson